1. Field of the Invention
This invention relates to a highly elastic sealing element of metal, or metal gasket, for the static, radial sealing of junctions and joints and in particular of flanged couplings.
2. Discussion of the Related Art
Elastic metal gaskets are compressed between surfaces to be sealed--or mating surfaces--and are elastically deformed in the process. In the gasket, the deformation creates a sealing pressure which increases up to a given point as the deformation progresses. For sealing static connections one can basically distinguish between two types of sealing devices.
For one, there are gaskets which lie flush against radial mating surfaces of the components to be connected and which are pressed together by an axial force. This is generally accomplished by a screw-on coupling. In this approach, the force of the screw-on action must be greater than the sum of the counterpressure force resulting from the internal pressure and the sealing force generated by the sealing pressure of the gasket. The integrity of the seal over time is a function of the gasket material used, the thermal expansion or the yield strain of the material or the tractive or compressive stress acting on the coupling for instance as a result of changes in the power applied in screwing the coupling together and thus in the compression force.
Then there are gaskets which lie flush against axial mating surfaces of two components to be connected and which are radially compressed between the latter. In this case the screw connection absorbs only the force of the internal pressure while the radial sealing force for the compression of the gasket is provided by the connecting hardware of the two components and is therefore basically independent of the axial connective force.
The state of the art has provided a multitude of gaskets suitable for either sealing method.
Nevertheless, as requirements become ever more demanding, the choice of sealing materials that lend themselves to the production of gaskets exposed to significant pressure differences or strong temperature fluctuations begins to dwindle rapidly and is often limited to metals.
A metal gasket usually consists of a material that is more easily deformable than that of the mating surfaces to be sealed. However, when pressed into position the gasket, while adapting to the shape of the mating surfaces, cannot compensate for major surface irregularities nor for additional deformative forces acting on the gasket since the deformability of a metal gasket is generally quite limited. This means that the use of metal gaskets is contingent on high surface quality of the mating surfaces and high precision in the geometry of the components.
For axial sealing purposes there exist more or less flexible metal gaskets which are adequate for meeting the aforementioned requirements. For example, there are flat dual-ring gaskets for axial sealing, such as those shown in Busak+Luyken's "Helicoflex" catalog, vol. 2/85, pages 8, 9, 10 and 18. Among the drawbacks of this design, besides the aforementioned, significantly greater screw-on connective force required to obtain a tight seal, is the danger of damage to the mating surfaces due to the frontal arrangement of the mating surfaces at the end of a component where, during handling, they are exposed to all kinds of mechanical impact.
For radial sealing purposes there have been flexible metal gaskets the installation of which requires a reasonable amount of force for deforming the metal gasket. The radial mating surfaces are relatively well protected against mechanical impact and the attainable integrity of the seal is not affected by the power applied in screwing the components together nor by variations in the connective force.
For example, DE-C-22 41 273 shows in its FIG. 5 a metal gasket for radial sealing in which the gasket, as it is being pressed in place, is radially deformed by the cone-shaped element preceding the mating surface of a component and is forced against the companion component. DE-C-37 13 071 on its part describes assembly parameters for the cone-shaped element of an insert serving as a static radial seal and makes reference to a gasket marketed under the trade name "Helicoflex".
The disadvantage of this type of gasket is that, when the coupling is assembled, the gasket must first be slipped onto a conical surface and then forced or compressed upon the latter to produce the initial radial stress necessary for obtaining a tight seal. The gasket then slides along at least one more sealing surface before the components are in their final position. Sliding the gasket onto the conical surface and on the sealing surface under full compressive stress conditions poses the danger of damage to the sealing or mating surface which promptly compromises or indeed negates the integrity of the seal. A particular problem is that it is not possible immediately after the assembly to determine whether and to what extent any damage was caused in the assembly process. When the coupling is disconnected, the gasket again slides along the sealing surface before it passes the cone and loses some of the compressive stress as it returns partly to its original shape. In general, however, when a gasket is mounted, it sustains a permanent plastic deformation and must be replaced. That in turn will be useful only if the sealing or mating surfaces are in good condition. If they are not, they must be reworked, i.e. resurfaced, which for instance in the case of pipeline flanges or cylinder head gaskets becomes a major project. Also, the friction involved in slipping on the gasket is such as to require a relatively strong effort in establishing the seal.